1. Field of the Invention
The present invention relates to a sealed threaded tubular connection under static stresses such as axial tension, axial compression, bending, internal or external pressure and a combination thereof.
2. Discussion of the Background
Such sealed threaded tubular connections, hereinafter also termed connections, may be produced by connecting a male element at the end of a first tubular component which may, for example, be a great length tube, and a female element at the end of a second tubular component which may, for example, be a great length tube or a coupling, each of said elements being provided with a metal sealing surface and being radially tightened against the metal sealing surface of the other element.
Such connections are used in particular to produce sealed casing strings or tubing strings for hydrocarbon wells or for similar wells such as geothermal wells, for example.
The metal (or metal-metal) sealing surfaces of the male and female elements of such connections are extremely critical zones which guarantee the tightness of the connection.
In hydrocarbon wells, such connections are subjected to various stresses such as tension, compression, bending and pressure which is either generated by the external environment, or generated by fluids moving inside the connections. Such diverse stresses may vary with time during, for example, the step for cementing casings (increase in external pressure) or during the production step (increase in internal pressure) or during maintenance operations (stop then restart of production) and act alone or in combination.
Such connections are not only expected to withstand such mechanical stresses, but also to remain sealed upon application thereof. For this reason, a large number of developments have been made in particular as regards connections employing metal/metal sealing surfaces. The general concept of such connections is to have two surfaces cooperating by tightening contact, one belonging to the male end of a first tubular component and the other to a female end of a second tubular component. The male and female ends each comprise a threaded zone enabling them to be connected by make up. Further, the sealing surfaces are dimensioned so that they can come into interference contact during make up, the interference contact resulting from radian tightening between the two sealing surfaces.
By way of example, document FR-2 913 746 proposes a threaded connection comprising a first and a second tubular component, each being provided with a respective male and female end, the male end comprising, on its outer peripheral surface, a threaded zone, a sealing surface and finishing in a terminal surface which is radially orientated with respect to the axis of the connection, the female end comprising, on its inner peripheral surface, a threaded zone cooperating by make up with the threaded zone of the male end, a sealing surface cooperating by tightening with the sealing surface of the male end and finishing in a terminal surface which is radially orientated with respect to the axis of the connection. The sealing surface of the female end is disposed on the inner peripheral surface of said end in a manner which is adjacent to the terminal surface. Between this sealing surface and the threaded zone, a zone is provided which has a reduced radial stiffness so that it can be deformed radially by a pressure which is exerted thereon. This reduced radial stiffness zone is obtained by reducing the annular section of the connection over a portion which is located between the threaded zone and the sealing surface of the female end. The reduction in the annular section is actually obtained by hollowing out a groove at the inner periphery. For this reason, this portion is capable of deforming radially when an external pressure is applied and for this reason generates extra elastic energy which enables the first and second sealing surfaces to be pressed together into tightening contact. It should also be noted that the zones which are thinner because of the presence of a groove recessed into the inner periphery of the female end may be considered to constitute an improvement in the case in which the threaded zone is of the “self-locking” type. In fact, that type of threading requires machining of a groove termed a “run in” groove the thickness of which is preferably at least equal to the height of the teeth to be machined and the length of which is preferably equal to at least half the lead. The “run in” groove acts to allow engagement and disengagement of cutting tools during machining of the threaded zone.
Thinning a portion of an annular section must be optimized in order to withstand pressure stresses and to provide the thinned portion with a sufficient elastic deformation range. This compromise, however, has limitations when the pressure exceeds the maximum elastic deformation threshold which is admissible by the groove. This may occur in the case in which the sealing surface is external, when the connection passes through pockets of fluids located at large depths. Similarly, when the sealing surface is internal, the value of the maximum pressure admissible by the groove may be exceeded when the fluid starts to move again at full speed after an interruption.